This is Fatimah Abdullah from Educative. Thank you for reaching out to us!

Yes, it is correct that we are using an array, therefore, it is understood that we can access each index in O(1) . However, this is not the standard implementation of an adjacency list. You might find some implementations using a linked list of linked lists. In that case, the complexity of the search will be O(VxV) . We mentioned indexing so that it is clear that this only applies if an array is used. I hope this clears up your confusion.

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